In the electric meter box art it is becoming increasingly necessary to provide positive means for locking closed the cover of the meter box, to prevent unauthorized persons from gaining access to the terminals inside the box. Locking is often accomplished by the use of a so-called barrel lock or plunger lock, such as is shown in my U.S. Pat. No. 3,186,196 issued June 1, 1965.
This lock comprises a housing and a pair of balls which are moved outwardly into the locking position by an internal axially movable plunger. The plunger is spring biased to the locking position, and is moved to the unlocking position by the insertion of an expandable tool into the end of a hollow stem of the plunger. The tool frictionally grips the internal walls of the stem so that tension can be applied to the plunger to pull it, against the force of the spring, to the unlocking position.
However, it has been found that it is possible to jam an article, such as a wire with a suitably bent end, into the stem cavity, and with sufficient perseverance, to obtain sufficient frictional engagement with the internal stem wall to pull the plunger to the unlocking position.
To prevent the possibility of defeating a lock of this type, I have disclosed and claimed in U.S. patent application Ser. 700,078, filed 06/28/76, a lock of this type having a separate tool-engaging member in a recess on the rear end of the plunger, said member having a pin protruding through a cover plate on the rear end of the recess. The separate tool-engaging member is spring-biased against the bottom of a recess in the plunger. When an axial pulling force is applied to the pin, it pulls the plunger rearwardly in the usual manner to release the locking means. However, when a pushing force is applied to the pin, it is forced into the recess through the opening in the cover plate to become inaccessible, and preventing an unauthorized tool from gripping engagement therewith.
However, it has been found possible, in some cases, to open a lock of the type described in the above-identified application by inserting a bent end of a wire into one of the rearmost coils of the spring that biases the pin to the locked position, and pulling to compress the spring so that the pin can move to the unlocked position.